The present invention relates to an interband single-electron tunnel transistor and integrated circuit utilizing a single-electron tunneling phenomenon, or more particularly, an interband single-electron tunneling phenomenon between a valence band and a conduction band in a p-n junction.
It is believed that about the time when the MOS device would have a channel length region of 1/4 .mu.m, further fine processing by integration technique for the conventional VLSI would become difficult, as disclosed in, for example, Journal of Physics of Japan, Vol. 46, No. 5, (1991), pp. 352-359 and TECH. REPORTS OF IECIE, November (1990), pp. 1-8, SDM90-119. Since many advances in integrated circuits are supported by an unceasing advance in fine processing, the above hindrance will become a great issue in the near future. In order to solve such a problem, devices utilizing quantum effects have been proposed actively.
There are many kinds of devices utilizing quantum effects. The most general device is an electron-wave interference device which utilizes the wave property of electron. In the electron-wave interference device, quantum-mechanical electron waves are made to interfere with each other to strengthen or weaken themselves so as to realize a switching operation. However, the prior electron-wave interference device involves several problems. In Physics Today, October (1989), pp. 119-121, it is pointed out that the characteristics of an electron-wave interference device greatly change depending upon a minute change of its device structure and it is of view that the application of the electron-wave interference device to an integrated circuit is difficult. Also, in the above Journal of Physics Society of Japan, Vol. 46, No. 5, (1991), pp. 352-359, it is pointed out that the ratio of a conductance of an electron-wave interference device in its ON state to that in its OFF state is small by several orders as compared with the conventional MOS device and it is of view that the application of the electron-wave interference device to an integrated circuit is difficult.
I order to solve the above problems of the electron-wave interference device, there has been proposed a single-electron tunnel transistor which utilizes the particle property of electron. As shown by, for example, IEEE, Trans. Magnetics, MAG-23 (1987), pp. 1142-1145 and Parity, Vol. 5, No. 10, (1990), pp. 22-28, the single-electron tunnel transistor includes as its fundamental constituent element a microcapacity having an electrostatic capacitance on the order of f.sub.F (femtofarad=10.sup.-15 F) and utilizes a quantum phenomenon peculiar to the microcapacity called Coulomb blockade.
The microcapacity for forming the single-electron tunnel transistor has a structure in which an insulating layer is sandwiched between two conducting materials. The insulating layer is made thin so as to allow the tunneling of an electron between the two conducting materials. In such a microcapacity, a phenomenon that the tunneling of an electron from one of the conducting materials to the other through the insulating layer is inhibited in a temperature range of T&lt;e.sup.2 /(2Ck) and in a potential difference range of -e/(2C)&lt;V&lt;e/(2C), is called Coulomb blocdage. Herein, T is the temperature, V the potential difference across the microcapacity, e the charge amount of one electron, C the electrostatic capacitance of the microcapacity, and k the Boltzmann constant. Accordingly, if the electrostatic capacitance of the microcapacity is made small by making the area of the capacity small, the Coulomb blockade can be realized in a higher state in temperature and in a higher state in potential difference or voltage across the capacity.
When the potential difference across the microcapacity exceeds a value defined by the above condition of Coulomb blockade, a release from the Coulomb blockade is made so that single-electron tunneling occurs between conducting materials. In a single-electron tunnel transistor including such a microcapacity formed as a fundamental constituent element, the flowing of current between the source and the drain is inhibited due to the Coulomb blockade when a gate voltage is turned off and is allowed because of a release from the Coulomb blockade when the gate voltage is turned on. In the single-electron tunnel transistor, the ratio of a conductance in an ON state to that in an OFF state is large as compared with the electron-wave interference device and the characteristics of the device are not almost influenced by a minute change in structure.
In the conventional single-electron tunnel transistor, an electron passes through the insulating layer each time the gate voltage is turned on. In general, the passage of electrons through an insulating layer causes the deterioration of the insulating layer. In the conventional single-electron tunnel transistor, therefore, there arises a problem that since an electron passes through the insulating layer each time the gate voltage is turned on, the deterioration of the insulating layer is advanced, thereby remarkably deteriorating the reliability of the device. Also, in the conventional single-electron tunnel transistor, since the microcapacity is formed by sandwiching the insulating layer between two conducting materials, the fabrication process is very complicated. Accordingly, it is supposed that many problems in fabrication process will arise in the case where an integrated circuit is to be formed.
Namely, in the conventional single-electron tunnel transistor, since an insulating layer which is a path of electrons is used as a portions of the microcapacity, the lifetime of the device is shortened and the reliability thereof is deteriorated. Also, owing to the presence of the insulating layer, the fabrication process is complicated and it becomes difficult to form an integrated circuit.